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Show 1880.] SPECIES OF REITHRODON. 695 what more strongly made. As the ears also in R. typicus are decidedly longer than in R. cuniculoides, being 0*74 inch long as against 0 56, measured in each case from the base of the outer edge, and the tarsi are shorter (1*12 against 1*26 without the claws), I do not think that at present we are justified in assuming the existence of intermediate forms, though I have but little doubt that such will yet be found to occur. I exhibit a drawing (fig. 3, p. 694) of what remains of the skull of the type of R. typicus, which has only recently been taken out of the skin, and therefore was not figured with the others in the Zoology of the voyage of H.M.S. « Beagle.' As to the localities from which specimens of this genus have been obtained, I may mention that, besides the types of Waterhouse's three species, the British Museum possesses a specimen in spirit of R. chinchilloides, obtained by the Antarctic Expedition of 1842 close to Cape Horn, and a skin of the same species collected by Mr. T. Bridges in the province of Mendoza, Central Chili. There is also a specimen of R. typicus recorded from Parana, La Plata, by Burmeister l. As we have thus two specimens in spirit belonging to the genus Beithrodon, besides a good series of Sigmodon and Hesperomys, I have thought it worth while to examine and compare the alimentary canals of specimens belonging to these genera. In the first place I exhibit a drawing (fig. 4) of the caecum Caecum of Beithrodon alstoni. of R. alstoni ; it is of the natural size, and shows the shape of the organ very well. In R. chinchilloides the caecum is very 1 Reise durch die La Plata-Staaten, p. 413 (1861). |
